=for comment
This document is in Pod format. To read this, use a Pod formatter,
like "perldoc perlpod".
=head1 NAME
X X
perlpod - the Plain Old Documentation format
=head1 DESCRIPTION
Pod is a simple-to-use markup language used for writing documentation
for Perl, Perl programs, and Perl modules.
Translators are available for converting Pod to various formats
like plain text, HTML, man pages, and more.
Pod markup consists of three basic kinds of paragraphs:
L,
L, and
L.
=head2 Ordinary Paragraph
X
Most paragraphs in your documentation will be ordinary blocks
of text, like this one. You can simply type in your text without
any markup whatsoever, and with just a blank line before and
after. When it gets formatted, it will undergo minimal formatting,
like being rewrapped, probably put into a proportionally spaced
font, and maybe even justified.
You can use formatting codes in ordinary paragraphs, for B,
I, C, L, and more. Such
codes are explained in the "L"
section, below.
=head2 Verbatim Paragraph
X X
Verbatim paragraphs are usually used for presenting a codeblock or
other text which does not require any special parsing or formatting,
and which shouldn't be wrapped.
A verbatim paragraph is distinguished by having its first character
be a space or a tab. (And commonly, all its lines begin with spaces
and/or tabs.) It should be reproduced exactly, with tabs assumed to
be on 8-column boundaries. There are no special formatting codes,
so you can't italicize or anything like that. A \ means \, and
nothing else.
=head2 Command Paragraph
X
A command paragraph is used for special treatment of whole chunks
of text, usually as headings or parts of lists.
All command paragraphs (which are typically only one line long) start
with "=", followed by an identifier, followed by arbitrary text that
the command can use however it pleases. Currently recognized commands
are
=pod
=head1 Heading Text
=head2 Heading Text
=head3 Heading Text
=head4 Heading Text
=over indentlevel
=item stuff
=back
=begin format
=end format
=for format text...
=encoding type
=cut
To explain them each in detail:
=over
=item C<=head1 I>
X<=head1> X<=head2> X<=head3> X<=head4>
X X X X
=item C<=head2 I>
=item C<=head3 I>
=item C<=head4 I>
Head1 through head4 produce headings, head1 being the highest
level. The text in the rest of this paragraph is the content of the
heading. For example:
=head2 Object Attributes
The text "Object Attributes" comprises the heading there.
The text in these heading commands can use formatting codes, as seen here:
=head2 Possible Values for C
Such commands are explained in the
"L" section, below.
=item C<=over I>
X<=over> X<=item> X<=back> X X X
=item C<=item I>
=item C<=back>
Item, over, and back require a little more explanation: "=over" starts
a region specifically for the generation of a list using "=item"
commands, or for indenting (groups of) normal paragraphs. At the end
of your list, use "=back" to end it. The I option to
"=over" indicates how far over to indent, generally in ems (where
one em is the width of an "M" in the document's base font) or roughly
comparable units; if there is no I option, it defaults
to four. (And some formatters may just ignore whatever I
you provide.) In the I in C<=item I>, you may
use formatting codes, as seen here:
=item Using C to Control Buffering
Such commands are explained in the
"L" section, below.
Note also that there are some basic rules to using "=over" ...
"=back" regions:
=over
=item *
Don't use "=item"s outside of an "=over" ... "=back" region.
=item *
The first thing after the "=over" command should be an "=item", unless
there aren't going to be any items at all in this "=over" ... "=back"
region.
=item *
Don't put "=headI" commands inside an "=over" ... "=back" region.
=item *
And perhaps most importantly, keep the items consistent: either use
"=item *" for all of them, to produce bullets; or use "=item 1.",
"=item 2.", etc., to produce numbered lists; or use "=item foo",
"=item bar", etc.--namely, things that look nothing like bullets or
numbers.
If you start with bullets or numbers, stick with them, as
formatters use the first "=item" type to decide how to format the
list.
=back
=item C<=cut>
X<=cut> X
To end a Pod block, use a blank line,
then a line beginning with "=cut", and a blank
line after it. This lets Perl (and the Pod formatter) know that
this is where Perl code is resuming. (The blank line before the "=cut"
is not technically necessary, but many older Pod processors require it.)
=item C<=pod>
X<=pod> X
The "=pod" command by itself doesn't do much of anything, but it
signals to Perl (and Pod formatters) that a Pod block starts here. A
Pod block starts with I command paragraph, so a "=pod" command is
usually used just when you want to start a Pod block with an ordinary
paragraph or a verbatim paragraph. For example:
=item stuff()
This function does stuff.
=cut
sub stuff {
...
}
=pod
Remember to check its return value, as in:
stuff() || die "Couldn't do stuff!";
=cut
=item C<=begin I>
X<=begin> X<=end> X<=for> X X X
=item C<=end I>
=item C<=for I I>
For, begin, and end will let you have regions of text/code/data that
are not generally interpreted as normal Pod text, but are passed
directly to particular formatters, or are otherwise special. A
formatter that can use that format will use the region, otherwise it
will be completely ignored.
A command "=begin I", some paragraphs, and a
command "=end I", mean that the text/data in between
is meant for formatters that understand the special format
called I. For example,
=begin html

This is a raw HTML paragraph

=end html
The command "=for I I"
specifies that the remainder of just this paragraph (starting
right after I) is in that special format.
=for html

This is a raw HTML paragraph

This means the same thing as the above "=begin html" ... "=end html"
region.
That is, with "=for", you can have only one paragraph's worth
of text (i.e., the text in "=foo targetname text..."), but with
"=begin targetname" ... "=end targetname", you can have any amount
of stuff in between. (Note that there still must be a blank line
after the "=begin" command and a blank line before the "=end"
command.)
Here are some examples of how to use these:
=begin html
Figure 1.
=end html
=begin text
---------------
| foo |
| bar |
---------------
^^^^ Figure 1. ^^^^
=end text
Some format names that formatters currently are known to accept
include "roff", "man", "latex", "tex", "text", and "html". (Some
formatters will treat some of these as synonyms.)
A format name of "comment" is common for just making notes (presumably
to yourself) that won't appear in any formatted version of the Pod
document:
=for comment
Make sure that all the available options are documented!
Some I will require a leading colon (as in
C, or
C),
to signal that the text is not raw data, but instead I Pod text
(i.e., possibly containing formatting codes) that's just not for
normal formatting (e.g., may not be a normal-use paragraph, but might
be for formatting as a footnote).
=item C<=encoding I>
X<=encoding> X
This command is used for declaring the encoding of a document. Most
users won't need this; but if your encoding isn't US-ASCII or Latin-1,
then put a C<=encoding I> command early in the document so
that pod formatters will know how to decode the document. For
I, use a name recognized by the L
module. Examples:
=encoding utf8
=encoding koi8-r
=encoding ShiftJIS
=encoding big5
=back
C<=encoding> affects the whole document, and must occur only once.
And don't forget, when using any other command, that the command lasts up
until the end of its I, not its line. So in the
examples below, you can see that every command needs the blank
line after it, to end its paragraph.
Some examples of lists include:
=over
=item *
First item
=item *
Second item
=back
=over
=item Foo()
Description of Foo function
=item Bar()
Description of Bar function
=back
=head2 Formatting Codes
X X
X X
In ordinary paragraphs and in some command paragraphs, various
formatting codes (a.k.a. "interior sequences") can be used:
=for comment
"interior sequences" is such an opaque term.
Prefer "formatting codes" instead.
=over
=item CtextE> -- italic text
X X<< IZ<><> >> X X
Used for emphasis ("Ccareful!E>") and parameters
("CLABELE>")
=item CtextE> -- bold text
X X<< BZ<><> >> X X
Used for switches ("C-nE switch>"), programs
("CchfnE for that>"),
emphasis ("Ccareful!E>"), and so on
("CautovivificationE>").
=item CcodeE> -- code text
X X<< CZ<><> >> X X
Renders code in a typewriter font, or gives some other indication that
this represents program text ("Cgmtime($^T)E>") or some other
form of computerese ("Cdrwxr-xr-xE>").
=item CnameE> -- a hyperlink
X X<< LZ<><> >> X X
There are various syntaxes, listed below. In the syntaxes given,
C, C, and C cannot contain the characters
'/' and '|'; and any '' should be matched.
=over
=item *
CnameE>
Link to a Perl manual page (e.g., CNet::PingE>). Note
that C should not contain spaces. This syntax
is also occasionally used for references to Unix man pages, as in
Ccrontab(5)E>.
=item *
Cname/"sec"E> or Cname/secE>
Link to a section in other manual page. E.g.,
Cperlsyn/"For Loops"E>
=item *
C/"sec"E> or C/secE>
Link to a section in this manual page. E.g.,
C/"Object Methods"E>
=back
A section is started by the named heading or item. For
example, Cperlvar/$.E> or Cperlvar/"$."E> both
link to the section started by "C<=item $.>" in perlvar. And
Cperlsyn/For LoopsE> or Cperlsyn/"For Loops"E>
both link to the section started by "C<=head2 For Loops>"
in perlsyn.
To control what text is used for display, you
use "Ctext|...E>", as in:
=over
=item *
Ctext|nameE>
Link this text to that manual page. E.g.,
CPerl Error Messages|perldiagE>
=item *
Ctext|name/"sec"E> or Ctext|name/secE>
Link this text to that section in that manual page. E.g.,
Cpostfix "if"|perlsyn/"Statement Modifiers"E>
=item *
Ctext|/"sec"E> or Ctext|/secE>
or Ctext|"sec"E>
Link this text to that section in this manual page. E.g.,
Cthe various attributes|/"Member Data"E>
=back
Or you can link to a web page:
=over
=item *
Cscheme:...E>
Ctext|scheme:...E>
Links to an absolute URL. For example, Chttp://www.perl.org/E> or
CThe Perl Home Page|http://www.perl.org/E>.
=back
=item CescapeE> -- a character escape
X X<< EZ<><> >> X X
Very similar to HTML/XML C;> "entity references":
=over
=item *
CltE> -- a literal E (less than)
=item *
CgtE> -- a literal E (greater than)
=item *
CverbarE> -- a literal | (Itical I)
=item *
CsolE> -- a literal / (Iidus)
The above four are optional except in other formatting codes,
notably C...E>, and when preceded by a
capital letter.
=item *
ChtmlnameE>
Some non-numeric HTML entity name, such as CeacuteE>,
meaning the same thing as C in HTML -- i.e., a lowercase
e with an acute (/-shaped) accent.
=item *
CnumberE>
The ASCII/Latin-1/Unicode character with that number. A
leading "0x" means that I is hex, as in
C0x201EE>. A leading "0" means that I is octal,
as in C075E>. Otherwise I is interpreted as being
in decimal, as in C181E>.
Note that older Pod formatters might not recognize octal or
hex numeric escapes, and that many formatters cannot reliably
render characters above 255. (Some formatters may even have
to use compromised renderings of Latin-1 characters, like
rendering CeacuteE> as just a plain "e".)
=back
=item CfilenameE> -- used for filenames
X X<< FZ<><> >> X X
Typically displayed in italics. Example: "C.cshrcE>"
=item CtextE> -- text contains non-breaking spaces
X X<< SZ<><> >> X
X
This means that the words in I should not be broken
across lines. Example: S$x ? $y : $zE>>.
=item Ctopic nameE> -- an index entry
X X<< XZ<><> >> X X
This is ignored by most formatters, but some may use it for building
indexes. It always renders as empty-string.
Example: Cabsolutizing relative URLsE>
=item CE> -- a null (zero-effect) formatting code
X X<< ZZ<><> >> X X
This is rarely used. It's one way to get around using an
EE...E code sometimes. For example, instead of
"CltE3>" (for "NE3") you could write
"CEE3>" (the "ZEE" breaks up the "N" and
the "E" so they can't be considered
the part of a (fictitious) "NE...E" code).
=for comment
This was formerly explained as a "zero-width character". But it in
most parser models, it parses to nothing at all, as opposed to parsing
as if it were a E or E, which are REAL zero-width characters.
So "width" and "character" are exactly the wrong words.
=back
Most of the time, you will need only a single set of angle brackets to
delimit the beginning and end of formatting codes. However,
sometimes you will want to put a real right angle bracket (a
greater-than sign, '>') inside of a formatting code. This is particularly
common when using a formatting code to provide a different font-type for a
snippet of code. As with all things in Perl, there is more than
one way to do it. One way is to simply escape the closing bracket
using an C code:
C=E $b>
This will produce: "C=E $b>"
A more readable, and perhaps more "plain" way is to use an alternate
set of delimiters that doesn't require a single ">" to be escaped.
Doubled angle brackets ("<>") may be used I For example, the following will
do the trick:
X
C<< $a <=> $b >>
In fact, you can use as many repeated angle-brackets as you like so
long as you have the same number of them in the opening and closing
delimiters, and make sure that whitespace immediately follows the last
''
of the closing delimiter. (The whitespace is ignored.) So the
following will also work:
X
C<<< $a <=> $b >>>
C<<<< $a <=> $b >>>>
And they all mean exactly the same as this:
C=E $b>
The multiple-bracket form does not affect the interpretation of the contents of
the formatting code, only how it must end. That means that the examples above
are also exactly the same as this:
C<< $a E=E $b >>
As a further example, this means that if you wanted to put these bits of
code in C (code) style:
open(X, ">>thing.dat") || die $!
$foo->bar();
you could do it like so:
C<<< open(X, ">>thing.dat") || die $! >>>
C<< $foo->bar(); >>
which is presumably easier to read than the old way:
CEthing.dat") || die $!>
Cbar();>
This is currently supported by pod2text (Pod::Text), pod2man (Pod::Man),
and any other pod2xxx or Pod::Xxxx translators that use
Pod::Parser 1.093 or later, or Pod::Tree 1.02 or later.
=head2 The Intent
X
The intent is simplicity of use, not power of expression. Paragraphs
look like paragraphs (block format), so that they stand out
visually, and so that I could run them through C easily to reformat
them (that's F7 in my version of B, or Esc Q in my version of
B). I wanted the translator to always leave the C and C and
C quotes alone, in verbatim mode, so I could slurp in a
working program, shift it over four spaces, and have it print out, er,
verbatim. And presumably in a monospace font.
The Pod format is not necessarily sufficient for writing a book. Pod
is just meant to be an idiot-proof common source for nroff, HTML,
TeX, and other markup languages, as used for online
documentation. Translators exist for B, B,
B